Homeostasis and the Autonomic Nervous System

• All autonomic nerves are motor nerves that regulate organs without conscious control.

• The autonomic nervous system maintains homeostasis by adapting your body to the external environment

• Composed of two distinct units:

1. Sympathetic Nervous System2. Parasympathetic Nervous System

Sympathetic system

• Prepares the body for stress

Parasympathetic system• Restores normal body condions

Sympathetic Nerves:• Come from the

thoracic vertebrae, and lumbar vertebrae

Parasympathetic Nerves:

• Exit directly from the brain, or either the cervical, or caudal sections of the spinal cord

Vagus nerve• major cranial

nerve

• parasympathetic

• Branches of the vagus nerve regulate the heart, bronchi, liver, pancreas, and digestive tract

Organ Sympathetic Parasympathetic

Heart Increase heart rate Decrease heart rate

Digestive Decrease peristalsis Increase peristalsis

Liver Increases the release of glucose

Stores glucose

Eyes Dilates pupils Constricts pupils

Bladder Relaxes sphincter Contracts sphincter

Skin Increases blood flow Decreases blood flow

Adrenal gland Causes the release of epinephrine

No effect

Some Effects of the Autonomic Nervous System

Natural Painkillers

• Pain is interpreted in the substantia gelatinosa (SG) – grey matter in the dorsal spinal cord

• Upon stimulation, the SG produes a neurotransmitter that “informs” the injured tissue or organ of the damage

• The greater the amount of the pain neurotransmitter attached to the organ, the greater the perception of pain

• Endorphins and Enkephalins attach to receptor sites in the SG

Endorphins They are produced by the pituitary gland and the hypothalamus during strenuous exercise, excitement and pain. They resemble the opiates in their abilities to produce analgesia and a sense of well-being.

Endorphins work as "natural pain relievers", whose effects may be enhanced by other medications.